Würzburg Seminar on Quantum Field Theory and Gravity

The scale at which quantum gravity becomes manifest, the species scale, has recently been argued to take values parametrically lower than the Planck scale in certain regimes. In this talk I will discuss how black holes of vanishing horizon area (small black holes) allow us to relate three different physical manifestations of the species scale: (i) Near the small black hole core, a scalar field runs to infinite distance in moduli space, a regime in which the Swampland Distance Conjecture predicts a tower of exponentially light states, which lower the species scale. (ii) We integrate out modes in the tower and generate via Emergence a set of higher derivative corrections that become relevant at the species scale. (iii) Finally, higher derivative terms modify the black hole solution and grant it a non-zero, species scale sized stretched horizon, showcasing the species scale as the size of the smallest possible black hole describable in the effective theory. I will give special emphasis to the fascinating example of 10d Type IIA black holes with D0-brane charge. The emergence of the species scale horizon for D0-branes requires a non-trivial interplay of different 8-derivative terms in type IIA and M-theory, providing a highly non-trivial check of our unified description of the different phenomena associated to the species scale.